Pressure sensitive adhesives (PSAs) are used in many cases for long-term bonds even in a relatively large temperature range. For these applications acrylic PSAs are used with great preference. Besides their very good temperature stability these acrylic PSAs also possess further advantages, such as very low aging and also weathering under UV light and an oxygen-containing atmosphere, for example.
A further very important aspect is the optical transparency of the PSAs. Specifically a multiplicity of industrial applications in the electrical and electronics sector call for acrylic PSAs which still possess a high transparency even at a wavelength of 400 nm.
A further trend lies in the use of PSA tapes with very low solvent fractions. A suitable technology here is that known as the hotmelt technology, in which polyacrylate PSAs are freed from their solvent and subsequently coated from the melt. The coating operation is relatively trouble-free for acrylic hotmelt PSAs with low average molecular weight, as evidenced by the commercial acrylic hotmelt PSAs UV acResins™ from BASF AG. For a multiplicity of industrial applications, however, a high shear strength (high internal cohesion) is called for, which these hotmelt PSAs, however, are unable to fulfill.
It is an object of the invention, therefore, to specify a process for preparing a UV-crosslinking pressure sensitive adhesive which is to be processed from the melt, has a high UV transparency, possesses a low residual solvent fraction, and has a high internal cohesion after UV crosslinking. Furthermore, it is intended to specify a process for preparing a pressure sensitive adhesive of this type and also the use thereof as a pressure sensitive adhesive for an adhesive tape.